Rate allocation and rate control are integral components of modern video compression systems. Rate allocation is the function by which a bit target is allocated for coding a picture. Rate control is a mechanism by which the bit target is achieved during coding the picture.
A compressed bit stream may be able to satisfy specific bandwidth constraints that are imposed by the transmission or targeted medium through rate control. Rate control algorithms can try to vary the number of bits allocated to each picture so that the target bit rate is achieved while maintaining, usually, good visual quality. The pictures in a compressed video bit stream can be encoded in a variety of arrangements. For example, coding types can include intra-predicted, inter-predicted, and bi-predicted slices.